The agency will detour approximately 50 buses from the start of service and until about 3 p.m. during the full marathon. Riders should anticipate delays and allow for extra time.

Here's some more information from an advisory the agency sent out today:

— In Downtown, buses will be rerouted to stops near Steel Plaza T station, where riders may transfer to the T for free. Routes normally serving Squirrel Hill and Oakland will not serve Oakland during the marathon, but a free shuttle will be available to take riders between the neighborhoods. Riders heading to Children’s Hospital from Downtown can use the rerouted 64 Lawrenceville-Waterfront bus route, since the 88 Penn won't reach the hospital because of street closures.

— Additional, smaller detours will be in effect in Downtown and on the North Side on Friday and Saturday for marathon events.

— On Sunday, light rail service will begin around 4 a.m. and both inclines will open at 5 a.Riders should anticipate delays and allow for extra time.